An image sensor is a semiconductor device which converts an optical image into an electrical signal. Image sensors may be classified into charge coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors. CMOS image sensors may include a photodiode for sensing light and a CMOS logic circuit for processing the sensed light into an electrical signal to generate data. As the amount of light received in the photodiode increases, the photo sensitivity of the image sensor is enhanced. The photo sensitivity can be enhanced by increasing a fill factor (a ratio of the area of the photodiode to the entire area of the image sensor) or changing a traveling path of light incident on the area other than the photodiode such that the light is condensed into the photodiode. An example of light-condensing techniques is formation of an array of micro lenses. Micro lenses such as convex micro lenses composed of a material having high light transmissivity, are formed over the photodiode so that incident light can be refracted through the micro lenses to thereby radiate a larger quantity of light toward the photodiode area. In this case, light parallel to the optic axis of the micro lens is refracted by the micro lens to form a focal point at a certain position of the optic axis.
An image sensor includes a photodiode, an interlayer insulation layer, a color filter, a micro lens and the like. The photodiode senses light and converts the sensed light into an electrical signal. The interlayer insulation layer is provided for insulation between metal lines. The color filter represents three primary colors (RGB) of light and the micro lens condenses light into the photodiode.
As illustrated in example FIG. 1, a CMOS image sensor may include interlayer insulation layer 30 formed on and/or over semiconductor substrate 10 having a plurality of photodiodes 20. RGB color filter layers 40 are formed on and/or over interlayer insulation layer 30 corresponding to photodiodes 20. Planarization layer 50 is formed on and/or over RGB color filter layers 40 to planarize a nonuniform surface layer of color filter layers 40. An array of micro lenses 60 are formed on and/or over planarization layer 50 corresponding to photodiodes 20 and color filter layers 40.
In such a CMOS image sensor, however, an oxide film for forming the micro lenses is not dense and may produce a plurality of pin holes. The pin holes allow an etching solution to infiltrate into the oxide film in a subsequent etching process, thereby causing peeling of the micro lenses. Further, after the oxide film is etched, in a subsequent sawing process, particles may be stuck in the micro lenses, thereby causing contamination of the micro lenses.